1. Field of the Invention
The present invention relates to an outerrace of a universal joint having cross grooves, which for example, is used to connect a reduction gear mechanism and a drive shaft at a drive wheel axle of independent suspension type of an automobile, and process and apparatus for producing that outerrace.
2. Description of the Prior Art
The cross groove type joint having cross grooves of the prior art is a universal one, in which six balls 3 are loosely fitted between a generally cylindrical innerrace 1 connected to the journal of a shaft and an outerrace 2 accommodating the innerrace 1 and are retained in a cage 4, as shown in FIGS. 1 and 2. This universal joint is formed in the outer circumference of the innerrace 1 and in the inner face of the cylindrical portion of the outerrace 2 with six cross grooves 5 which are symmetrically inclined at an equal angle with respect to one another for receiving the balls 3 thereby to effect a uniform motion and proper axial movement. Moreover, the conventional outerrace of the universal joint of the above-specified kind is composed of two parts, i.e., the cylindrical member having the cross grooves and a shaft member. This outerrace is generally classified into one of the type in which bolts 6 are inserted into bolt holes 7 to fasten a cylindrical member 8 and a shaft member 9 through a clip 10, as shown in FIGS. 1 and 2, and the other of the type in which a cylindrical member 8' and a shaft member 9' are frictionally welded, as shown in FIG. 3. In the conventional joint shown in FIG. 1, incidentally , a boot 12 is fitted on a seal adaptor 11 attached to the cylindrical member 8 and is fastened by a boot band 13 to seal the inside of the joint.
In the case of the outerrace of either type, the cross grooves 5 are formed one by one or two by two either by a cutting work (e.g., a broaching work) or by a grinding work. As a result, the forming takes a long time resulting in low productivity which raises production cost of the outerrace. In addition, the cross grooves formed by the cutting work are not always sufficient in strength or the like. On the one hand, the outerrace of the bolt-fastened type, as in the aforementioned example of the prior art, not only has a problem of looseness of the bolts but also requires the bolt holes so that it generally has its external diameter increased thereby increasing its weight.
On the other hand, the outerrace of the frictionally welded type requires a welding margin and has a welding fin and there results sometimes expansion and deformation due to the welding heat. In the welding operation, moreover, the cylindrical member and the shaft member may be misaligned with each other. Thus, the outerrace has a problem in precision.